The present invention relates generally to die structures used in conjunction with metal working presses, and more particularly relates to methods and apparatus for transporting a die structure to and from a metal working press.
In conventional metal stamping operations, selected portions of a sheet of metal are punched out and removed utilizing a punch die structure removably interconnected to the opposed bed and vertically movable ram portions of a metal working press. The typical prior art punch die includes an upper die section positioned above a die shoe and connected to the shoe, for vertical movement relative thereto, by leader pin members. Projecting downwardly from the underside of the die shoe are two or more spaced apart, parallel support base members, usually referred to in the press art simply as "parallels". With the punch die operatively connected to the press, the metal-forming operation is carried out by positioning the metal sheet atop the die shoe and then downwardly moving the press ram to drive the upper die section into engagement with the metal sheet.
Since a conventional punch die typically weighs between 1,000 and 10,000 pounds or more, it is understandably difficult to move from its storage location to the press and back again after its use. To facilitate the transport of the die structure it has been conventional practice to attach a large metal base plate to the underside of the die parallels. During storage of the overall die structure, the base plate is supported atop the upper side surface of a storage platform into which liftable roller structures are recessed To move the die to its associated press, a specially designed die cart is used, the die cart having similarly recessed, liftable roller structures on its top side surface.
When the die is to be used, the cart is rolled up to the die storage platform, and the recessed roller structures of both the platform and the cart are elevated so that the die can be rolled along the raised platform surface rollers onto the raised rollers of the cart. The cart rollers are then lowered so that the base plate of the die rests directly on the flat top surface of the cart. After this is done, the cart is rolled to the punch press adjacent the press bed which is conventionally provided with liftable roller structures recessed into its top surface.
To transfer the die onto the press bed, the cart and press bed rollers are raised, and the die is rolled off the cart and onto the elevated bed rollers which are then lowered so that the bottom die support plate rests upon the flat upper surface of the press bed. Finally, the upper and lower die sections are respectively anchored to the press ram and the press bed to ready the press for operation.
As can readily be imagined, this previous necessity of providing recessed, liftably roller systems in die storage platforms, die carts and press beds to facilitate die changeout undesirably adds considerable expense and complexity to the overall punch press operation and requires that all three of these structures be of a customized construction. Additionally, the requirement for the large base plate secured to the undersides of the die parallels adds considerable weight and expense to each individual die structure and can undesirably add to the time and expense associated with routine maintenance thereof.
Various proposals have been made in the prior art to eliminate the necessity for providing recessed roller structures in the die storage platforms, the die transport cart, and the press bed by utilizing die-supporting structures, referred to as bolsters or carriages, which basically comprise a platform having wheels or rollers operatively secured to its underside. The bottom plate of a die structure is suitably anchored to the top of the bolster or carriage platform, and the platform wheels are positioned in tracks which lead to and from the press bed. To load a particular bed onto its associated press, the bolster is simply wheeled along the tracks until the bolster-supported die is operatively positioned on the press bed. The die and its bolster are then suitably clamped in place on the press bed.
A variety of structures are provided for lowering the underside of the bolster platform onto the top side of the press bed. For example, portions of the track sections extending across the press bed may be selectively lowered as representatively shown in U.S. Pat. No. 3,422,660 to Countess, Jr. et al and U.S. Pat. No. 3,986,448 to Seyfried et al. Alternatively, the bolster wheels may be spring-biased downwardly from the bolster platform, and the bolster platform subsequently clamped downwardly to overcome the wheel spring force, as illustrated in U.S Pat. No. 3,456,481 to Zeitlin.
U.S. Pat. No. 4,301,673 to Yonezawa discloses downwardly recessed wheels in the top of a bolster platform which may be raised to facilitate the rolling onto and off of the bolster platform of the die structure which it supports. Other disclosures of wheeled die bolster structures are present in U.S. Pat. No. 2,996,025 to Georgeff, and U.S. Pat. Nos. 3,229,791 and 3,306,185 to Soman.
A number of prior art bolsters, having platforms to which the bottom die plate is fixedly secured, are provided with vertically movable wheel structures as alternatives to collapsible track sections and the like to permit the bolster platform to be lowered onto and raised upwardly from the press bed top surface. For example, U.S. Pat. No. 3,422,662 to Geuss discloses a wheeled, die-supporting bolster secured to the underside of a die set. Lowerable sets of wheels are provided in side edge grooves of the bolster platform and are lowerable by fluid cylinders, via pivotable brackets, to elevate the bottom side of the bolster platform. Separate lifting jack mechanisms are provided in the press bed to lift the bolster platform before its wheels are lowered. U.S. Pat. No. 3,368,479 to Gregorovich illustrates liftably bolster wheels which are actuated by a motor and gear system. U.S. Pat. No. 4,528,903 to Lerch discloses a die-supporting bolster/carriage provided with wheels that are pneumatically liftable and lowerable relative to the bolster platform via the operation of pistons received in cylinders formed in the bolster platform.
While the use of these and other wheeled bolster devices to facilitate die transport arguably represents improvements over recessed wheel or roller structures provided in die storage platforms, die carts and press beds, they still present various disadvantages in the overall transport of die structures to and from their associated presses. For example, all of the above-described wheeled bolster devices require the presence on the die structure which they support of the conventional large bottom plate. Additionally, the wheeled bolster devices referred to above add considerable weight, height, and expense to the die structures to which they are secured. Further, the wheel lifting structures provided on these conventional bolster and carriage devices are of a rather complex construction.
It can readily be seen from the foregoing that a need exists for improved apparatus, operable to rollingly transport a punch die to and from its associated press, which eliminates or at least substantially reduces the above-mentioned problems, limitations, and disadvantages associated with conventional rolling die transport apparatus of the general type described. It is accordingly an object of the present invention to provide such improved apparatus.